r = number of rows

r + 19 = number of seats in each row

r(r + 19) = 1170 ← total seats equals number of rows times number of seats in each row

r² + 19r = 1170 ← distributive

r² + 19r - 1170 = 0 ← subtracted 1170

(r + 45)(r - 26) = 0 ← factored

r + 45 = 0 or r - 26 = 0 ← set to zero

r = -45 or r = 26 ← solved

r + 19 ← number of seats in each row

= 26 + 19 ← substituted

= 45 ← added

45 seats in each row

*McGenius*

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